Communication satellites receive and transmit radio signals from and to the surface of the Earth. Although Earth-orbiting communications satellites have been in use for many years, providing adequate cooling and heat distribution for the thermally sensitive electronics components onboard such satellites continues to be a problem.
There are two primary sources of heat with which a satellite's thermal systems must contend. One source is solar radiation. Solar radiation can be absorbed by thermal insulation shields or readily reflected away from the satellite by providing the satellite with a suitably reflective exterior surface. A second source of heat is the electronics onboard the satellite. The removal of electronics-generated heat is more problematic since such heat must be collected from various locations within the satellite, transported to a site at which it can be rejected from the satellite, and then radiated into space.
Passive thermal panels can be used to dissipate heat from satellites. In one configuration, the passive thermal panel includes a lightweight honeycomb core that is sandwiched between two thin, stiff panels or “skins”.
These thermal panels typically have “heat pipes” embedded therein. The use of internal heat pipes enables components to be mounted on the surface of the panels. Well known in the art, the heat pipe is a closed chamber, typically in the form of tube, having an internal capillary structure which is filled with a working fluid. The operating-temperature range of the satellite sets the choice of working fluid; ammonia, ethane and propylene are typical choices. Heat input (i.e., from heat-generating electronics) causes the working fluid to evaporate. The evaporated fluid carries the heat towards a colder heat-output section, where heat is rejected as the fluid condenses. The rejected heat is absorbed by the cooler surfaces of the heat-output section and then radiated into space. The condensate returns to the heat input section (near to heat-generating components) by capillary forces to complete the cycle.
When two mechanically independent passive thermal panels need to be thermally coupled, such as to move heat from one panel to the next, an external “jumper” or thermal strap is used. The jumper, which is a segment of heat pipe disposed on the outside of the panel, provides a bridge to thermally couple the heat pipes within the adjacent panels. The jumper is coupled to the one of the panels via a bolted interface.
FIGS. 3A and 3B depict, via respective cross-sectional and top views, an arrangement in the prior art showing jumper heat pipe 386 with bolted interface 390 attached to passive thermal panel 301. FIG. 3A depicts passive thermal panel 300 having honeycomb core 370 and skins 372A and 372B. Heat pipe 380 is disposed within panel 301. Heat pipe 380 includes conduit 382, which contains working fluid, and flanged region 384. Jumper heat pipe 386 is bolted to the exterior of passive thermal panel 301. Jumper heat pipe 386 includes conduit 388, which contains working fluid, and flanged region 390.
In this illustration, bolts 392 extend through flanged region 384 of embedded heat pipe 380 and through flanged region 390 of jumper heat pipe 386. Nuts 394 lock the bolts to the flanges, thereby attaching jumper heat pipe 386 to panel 301.
Thermal interface material 396 is used between flanged region 384 of embedded heat pipe 380 and flanged region 390 of jumper heat pipe 386 to improve heat transfer across these surfaces. The jumper heat pipe is coupled in the same fashion to an adjacent passive thermal panel (not shown). In this manner, heat can be transferred from one passive thermal panel to an adjacent panel.
It will be appreciated from FIGS. 3A and 3B that the presence of the jumper and bolted interface prevents other components from being mounted to the panel at those locations.